Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$121.57	8.489%	$131.8901	$131.89	$131.90	$131.90
Purchase #2	$46.72	9.183%	$51.0103	$51.01	$51.00	$51.00
Purchase #3	$18.50	11.637%	$20.6528	$20.65	$20.65	$20.70
Purchase #4	$124.36	4.488%	$129.9413	$129.94	$129.95	$129.90
Purchase #5	$165.33	8.506%	$179.393	$179.39	$179.40	$179.40
Purchase #6	$59.85	4.545%	$62.5702	$62.57	$62.55	$62.60
Purchase #7	$6.54	11.323%	$7.2805	$7.28	$7.30	$7.30
7 purchase totals =	$542.87		$582.7382	$582.73	$582.75	$582.80